Applicant provides for a motor vehicle for applying a liquid--such as hot asphalt, to the spray path of a roadway through the use of two spray bars mounted at the rear thereof, the first to cover part of the roadway spray path and the second to cover the remainder of the roadway spray path.
Asphalt distributors are used to spray asphalt over a spray path of a roadway surface. This spray path is defined as the width of the intended liquid asphalt spray coverage area, and is typically one lane of a roadway.
Usually, an asphalt distributor has, at the rear thereof, a spray bar with a multiplicity of nozzles pointed downward. Heated liquid asphalt in the tank of the truck is drawn from the tank through a liquid asphalt pump and into the spray bar and shot through the downward pointed nozzles onto the spray path. In prior art liquid asphalt distributors, the multiplicity of nozzles from a single spray bar cover the entire spray path by applying the liquid from each nozzle in a fan shaped spray pattern. The nozzles are mounted to a manifold on the spray bar and the pressure in the manifold is controlled by a control panel to control the rate of application. Through the control panel, the operator can control the amount of liquid asphalt or other material applied to the spray path. However, the present systems are not able to, in a single spray bar, selectively vary the amount of liquid asphalt or other material applied to the spray path at different nozzles. That is, in the present liquid asphalt delivery systems, the operator will select a given coverage (for example, 0.4 gallons per square yard), and that application will be made across the entire spray path unless the user manually changes out nozzles on the spray bar to smaller or larger nozzles for less or more coverage. When this occurs, the nozzles that are either smaller or larger will, of course, apply more or less liquid asphalt than the remaining nozzles. However, it is time consuming to perform such a nozzle changeout and also, once it occurs, requires another changeout of nozzles should the operator desire yet a different application rate. In other words, the present asphalt distribution systems are limited in their flexibility due to the cumbersome nozzle changeout requirements to effect a different application rate.
One reason that operators desire to vary the application rate across a spray path is that along most spray paths there are typically sections where there is extensive pressure exerted by the tires of automobiles and other sections where there is less pressure exerted. If one were to observe traffic moving along a single lane (a typical spray path) they would see that most cars travel so they are "centered" in the middle of the lane and leave a few feet on either side for safety purposes. That is, drivers of vehicles tend to center the vehicles in the lane so that there is a region to each lane where the tires tend to travel and a region between and outside of those tire paths that are not as tire worn.
This fact is important for the purposes of, for example, sealing a road with liquid asphalt. Proper application rates are, in part, a function of subsequent pressure and, as stated above, there is greater pressure applied to certain areas of the spray path after the road has been treated than to other areas. The operator typically desires to apply less liquid asphalt to the tire path of the spray path then to the non-tire path areas so as to prevent subsequent bleeding. This is presently done by swapping out, from the single spray bar, the nozzles that fall over the wheel path with smaller nozzles. As noted above, this is time consuming and not very accurate. That is, it is hard to regulate liquid asphalt application by nozzle jet size when nozzles wear. Further, nozzle changes cannot be made "on the run"--that is, without stopping and swapping out to other, different sized nozzles. Thus, it can be seen that utility lies in providing a means for selectively varying the rate of application across a spray path to allow a different rate of application on the wheel path portion of the spray path as compared to the nonwheel path portion of the spray path. That is, a spray path (typically the width of one lane of traffic) has a wheel path portion and a nonwheel path portion. The wheel path portion is that area which, most of the time, bears the weight of the vehicles traveling over it. The nonwheel path portion is the remainder of the spray path. Utility lies, therefore, since the proper rate of application of liquid asphalt or other material to those two regions of the wheel path often differs, in providing for a liquid asphalt distribution system that will allow such a variable rate.